What is a Hypnic Jerk?

Also called sleep start, hypnagogic jerk or monoclonic jerk, a hypnic jerk puts the "falling" in "falling asleep."  You've experienced it.  You are drifting off to sleep when your body suddenly moves.  You may also see a flash of light or hear a very loud noise.  Many people (like me) also feel as if they've suddenly fallen from a great height.  Here's what you need to know about hypnic jerks.

Why Am I Having Hypnic Jerks?

You have them because you're human.  Although there have been many theories as to the exact cause of hypnic jerks, there has been no conclusive proof.

Is It A Serious Condition?

Although they are freaky as hell, hypnic jerks are not dangerous.  It is normal to experience them.  Unless they happen repeatedly throughout the night (a condition called intensified hypnic jerks) you do not need to see a doctor about them.  People who jerk violently or see flashes of light may fear that they have a mild epileptic condition, notes Fundamentals of Sleep Technology (Lippincott Williams & Wilkins, 2007).  If your doctor is not sure if you have epilepsy, you may need to spend a night at a sleep clinic in order to rule out epilepsy.

Can You Prevent These Things?

Not really.  Places like Wikipedia and even the generally reliable WiseGEEK list things people can try to prevent hypnic jerks, but there is no known cure for hypnic jerks.

Image of homeless sleeper in Vancouver by Jay Black/ Wikimedia Commons.